Effects of Age-1 Striped Bass Predation on Juvenile Fishes in Western Albemarle Sound

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Historically, adult river herring (Alosa pseudoharengus, Alosa aestivalis) and American shad (Alosa sapidissima) fisheries were economically important in Albemarle Sound. Stocks of these species are currently in decline while stock estimates for striped bass (Morone saxatilis) have increased 10-fold for the Albemarle Sound-Roanoke River stock since the early 1990s. The primary goal of this study was to quantify the diet, prey selectivity and the predatory impact of age-1 striped bass on juvenile river herring and American shad in 2002 and 2003. Similar estimates were produced for juvenile yellow perch (Perca flavescens), a species with an expanding fishery. Striped bass and prey samples were obtained from 443 beach seine and 171 purse seine hauls from May through October in 2002 and 2003. Age-1 striped bass were primarily piscivorous from May onward in both years. Alosa spp. were a small component of age-1 striped bass diet in summer months but dominated diet in early fall months. Age-1 striped bass fed randomly with respect to Alosa spp. abundance during the summer and selected for them during early fall months. During summer 2003, selectivity for yellow perch decreased with concomitant decreases in importance as a prey item. Field estimates of consumption rates ranged from 3 to 8 % body weight per day while bioenergetics model estimates of consumption ranged from 4 to 12 % in 2002 and 3 to 10% in 2003. Age-1 striped bass density, diet, prey sizes eaten, and consumption rates were used to calculate loss rates due to predation and were compared with total loss rates from catch curves. There was interannual variation in the effects of predation. Age-1 striped bass predation had a marked effect on juvenile American shad densities in 2002 but had little influence on their numbers in 2003. Conversely, age-1 striped bass predation explained none of the loss in juvenile yellow perch in 2002 but accounted for nearly all of the loss in 2003. Thus, predation by striped bass may explain at least some of the variability in year class strength for these species. In most cases, age-1 striped bass predation did not have a strong influence on juvenile alewife numbers. Juvenile blueback herring were preyed on but the relative predatory impact could not be determined because of apparent emigration into the study area. To better understand striped bass impacts on Alosa spp., future work should address movement of juvenile Alosa spp into and out of Albemarle Sound estuary.



trophic interactions, Albemarle Sound, river herring, fishes, eggers model, predation, American shad, yellow perch, consumption rates, striped bass, bioenergetics modeling





Fisheries and Wildlife Sciences